1. Field of the Invention
The present invention relates to a vehicle occupant safety system and more particularly to a method and system for determining the severity of a vehicle crash and controlling an occupant safety system in response to the crash severity.
2. Related Art
It is known in the art relating to vehicle safety systems to trigger a passenger safety restraint in response to a vehicle crash. Such systems typically include an accelerometer mounted on the vehicle to sense vehicle acceleration crash condition. A controller is operatively connected to the accelerometer to receive an acceleration signal. The controller analyzes the acceleration signal to determine the severity of the crash and then based on the analysis the controller activates the safety restraint as required. The controller may determine the severity of the crash by using various calculated values of velocity, crash displacement and energy.
Such vehicle safety systems often include an air bag that inflates and cushions a passenger in the event of a crash. It is particularly desirable for the air bag to be activated only when the crash conditions require such activation. Unnecessary activation of the air bag may startle and distract the driver and may require costly replacement work to be done. Thus, it is desirable to provide a system that can accurately discriminate between fire and non-fire events.
The present invention provides a method and system for controlling a vehicle safety system based upon crash severity.
In one embodiment, the method and system determines a predicted velocity from a sensed vehicle acceleration signal, compares the predicted velocity with a velocity threshold and activates the safety restraint, for example, an air bag, if the predicted velocity exceeds the velocity threshold.
The predicted velocity is the velocity of the passenger relative to the vehicle at a time equal to the present time plus the airbag inflation time. A high predicted velocity generally indicates a severe crash condition.
In another embodiment, the method and system determines a predicted velocity from a sensed vehicle acceleration signal, and compares the predicted velocity with a velocity threshold. The method and system also determines an acceleration peak time from the sensed acceleration signal, and compares the acceleration peak time with an acceleration peak time threshold and activates the safety restraint if the predicted velocity exceeds the velocity threshold and the acceleration peak time is less than the acceleration peak time threshold.
The acceleration peak time is the time period measured from the detection of a first predetermined maximum acceleration value, to a predetermined minimum acceleration value and to a second predetermined maximum acceleration value. The detection of maximum acceleration times indicates the contacting of the bumper and then the contacting of the radiator support area of the vehicle as the vehicle structure collapses. With a higher speed crash, the contacts occur closer in time than for a lower speed crash. By determining the time interval between the contacts, the present invention better discriminates between high and low severity crashes.
In another embodiment, the method and system determine a predicted velocity from a vehicle acceleration signal, and compares the predicted velocity with a velocity threshold. The method and system also determines an acceleration peak time from the vehicle acceleration signal, and compares the acceleration peak time with an acceleration peak time threshold. The method and system also determines from the sensed acceleration signal whether a pole crash event has occurred and activates the safety restraint if the predicted velocity exceeds the velocity threshold and the acceleration peak time exceeds the acceleration peak time threshold, and the acceleration signal indicates that a pole crash event has occurred.
These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings.